High-frequency circuit



G. REBER HIIGH FREQUENCY CIRCUIT July 8, 1947.

Filed Jan. l, 1944 @cieli/e 5rd/ Vozige j@ E, d@

Patented July 8, 1947 HIGH-FREQUENCYy CIRCUIT Grote Reber, Wheaton, Ill., assignor to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Application January 1, 1944, Serial No. 516,737

7 Claims.

My invention relates generally to quasi-optical and ultra high frequency circuits, and more particularly to radio frequency choke assemblies.

' It is an object of my invention to provide an improved radio frequency choke which is completely contained in the tuned circuit of a transformer.

A further object is to provide an improved ultra high radio frequency transformer having two coupling impedances in parallel so that both the plate and grid choke lines may be brought out separately without interaction between them, and that they may be made of optimum length.

A further object is to provide an improved radio frequency choke for ultra high frequency circuits which incorporates blocking and by-pass condensers which are advantageously located with respect to their necessary size.

A further object is to provide an improved ultra high frequency circuit structure usable as part of a wide band amplifier which ha-s high gain and small losses.

Other objects will appear from the following description, reference being had to the accompanying drawings, in which Fig. 1 is a central longitudinal sectional View of the improved assembly, and

Fig.l 2 is a schematic wiring diagram showing the lumped constant electrical circuit equivalent of the Iassembly shown in Fig. 1.

The circuit structure comprises an inner cross- T I having coaxial conductors I2 and I4 held therein by insulating spacers I6. One end of the conductor I2 is connected to a plate clip I8 while its other end is connected to a plate forming part of a by-pass condenser C3. The conductor I4 i-s similarly connected between a grid clip 22 and a plate 24, the laftter forming part of a bypass condenser C4.

Concentric with and surrounding the left leg loa of theT structure I0 is a plate line tube 26, whilea grid linetube 28 surrounds and vis concentric with the right band leg Ib of the cross-T I0. The tubes 26 and 28 are joined to tubular coupling stubs 30 and 32 which are concentric with and surround portions of the upper leg Ic and lower leg Ind, respectively. The stubs 30 and 32 are joined to the legs Ic and lud, respectively, by their end walls 33.

' The plate clip I8 is separated from the leg Illa by adielectric tube 36 thus forming a plate blocking condenser ACI. Similarly, the grid clip 22 is 'separated from the leg IllbV by a dielectric tube 31 to form a grid blockingcondenser C2.

" In the' equivalent lumped constant circuit dia- 2 gnam of Fig. 2, Cp and Lp represent the output capacity and plate lead inductance within the first tube of an amplifier of .which the structure of Fig. l forms the interstage coupling mesh.

f Cg and Lg similarly represent the input capacity and grid lead inductance within the second tube of the amplifier.

When the structure of Fig. 1 is thus used as the coupling between Itwo stages of an amplifier the +B potential source is connected to the plate 20 of condenser C3 while the grid bias negative voltage source i-s connected to the plate 24 forming part of condenser C4.

The nductance LI determines the plate tuned frequency and represents the impedance of plate line tube 26 and the leg Illa. Inductance L3 determines the grid tuned frequency and represents the impedance of the grid line tube 28 and the leg Ib. The parallel inductances L2 determine the gridto plate coupling, and thus the band width, and represent the impedances of the coupling stubs 30 and 32 with reference to the portions of legs Ille and Illd which they respectively surround.

The inductance L4 is the plate radio frequency choke and represents the impedance of the coaxial line comprising conductor I2 and legs Illa and Ind. Similarly, the inductance L5 constitutes the grid radio frequency choke and represents the impedance of the coaxial line comprising conductor I4 and the legsv Ib and IIlc.

Those portions of the legs Ille and lud which extend beyond the coupling stubs 30 and 32 are preferably made of such length that the lengths of the coaxial lines provided by conductors I2 and I4 (L4 and L5) are each one-quarter wave length at the midband frequency fl). The inductive reactance of plate choke is where Zt is characteristic impedance o-f concentric conductors I2 and I0a,n|0d (L4 in equivalent lumped circuit)- At midband frequency f, X4 will be infinite since In the foregoinggw is the angular velocity in radians per second, l is the length of ythe line in centimeters, vhis the wave length in centimeters, while v is the velocity of radiant energy propagation, namely, .3 X 1010 centimeters per second.

. 3 At the edges fl and f2 of the frequency band the choke impedance X4 will be Z4 tan and The impedance of the grid radio frequency choke comprising conductors I4 and lb, I0c (L5 in v equivalent lumped circuit) at the frequencies at;

the edge of the band may be computed by similar formulas. l 7

The characteristic impedance of the choke conductors l2 and Ib, llld may be of a Value in the order of 200 ohms and thusseyeral thousand" the other hand', the mainby-passv condensers C3 t' and' C4' are external of the structure, and, hence, may .be conveniently made relatively large so as to have the desired very low reactance.

The structure `illu.Strated isv designed for use inY an amplifier. fora wide frequency band, such as. a 1Q meeeeyele bandy inV a frequency range from. 1.90m 1,09). megneyeles. Within this range thestltueture: has. been found. to. provide high gain-.and affords very-.effective .ehelses to .prevent the radio freniueney from entering the potential Supply eireuits...

As. above pointednut, the. lengthsof the. choke extnsienslnav be varied te'make L4 and L5. eX- actly one-quarter wave length long, this being illustrated .infie-1; bythe. feet that the Vles .me

is longen than; enel .e mld, and, '.enrresn-endn1elr, the and line.` tube. glieissnertertnnn the ple-te line wie. 2.6.

it will. ne undergone these skilled inthe art that einer variations inthe det ef-.tnestrnetnre'rney'bemndewn de tinefrern. .the nndenlyins. nrineinlen .nime 1 .venbi9n- I., inerefere, denne, bv the. feller-ine nlnirne te, nllnde Wnhinfine; SeOne'QfIn-y invention all Snen medicatinsandvariati wherebysubstantially the results offmyinvenv on are obtained by substan tially thesarneor efq'uiv'alentA means..

1. An interstage coupling for an ultra high radio frequency amplifier comprising, a tubular cross-T, a pair of conductorsrespectively extending coaxially through adjacent legs of said cross- T, capacitative connections`A between each end of each 'of Asaid conductors and itsQadjaqent end portienof. said, eree'e'Saiiileapeetatire nonnen-- tions comprising "blocking *and7 byy-fpassv condensers, and tubular plate and grid line elements completely surrounding oppositely directed legs of said cross-T and partially -surrounding the intermediate legs thereof, said tubular plate and grid line elementsbeing interconnected and connected e. sa@ @emanadas ef Sad-creeer; the' exe nnseennntiennef? Seid. internement-'lees felrnine bien rnnenenneredinfreqnenny.ehnkes; the effeef tivelengths of said conductors beingsubstantially r, a coaxial tubular member surrounding opposite legs of said cross-T and surrounding portions only fof tlie intermediate cross-T legs, whereby the 4p'irtions of said intermediate cross-T legs which are-notsurrounded by said coupling lines form radiqfrequencyf choke extensions.

3.Y A'circuit structure for use in interstage coupl-ing of anj ultra high frequency amplier comprsing, a cross-T, a pair of conductors each extending coaxially through a pair of adjacent arms of said cross-T, a tubular grid line and tubular plate .line respectively surrounding oppositely directed `legs/of saidV cross-fl?,` couplingstubs surrounding portions of the. intermediate .legsl ofersaid cross-.Ts and connected Ltosaidtubular grid. and plate lines, a blocking condenser formedbyac'ap surrounding and.r insulated .fromthe end of. one of said opposed legs of said cross-T, asimilar blocking condenser at the outerendof the; other of said opposed legs of saidcressfTf. and vley-:Dess condensers formed at the lendseofV the intermediate legs of said crossfT, said byzpass condensers'each hnvingone. plete thereof formed by .a portionof 1he intermediate cross-.T leg;-

4,. An ultra; high frequency circuit; structureA for coupling the outputof a first; electron discharge device with Vthe input of a second electron discharge dev-ice,y saidv vices formingpartsofan amplifier, the combination of .a cross- T, a first coaxial conductor extending through adjacent lees of seid' Cross-.1%. a seeondeoexial .Conductor extending through the other two `legs of. said cross-T, caps secured to the ends of opposed legs of said cross-T, saidcaps being insulatedfrom the vaejaeerlt vend portionsof said cross-T klegs to form blocking condensers, the blocking com denser et the end ,of seid: irst Conductor being adapted to be connected to the output, vofysaid first. eleetlfendieeheree device and the blneking condenser` connected tov the second conductor .beine adapted te be eenneeted te thenpnt 0f seid Senond elentren discharge device. ley-nnss. nendensers connected respectively to.V the other ends einen @endenderespecteer. each-of sa@ by- Peas. 'COnnenSerS Cernnrnine @radially-extending flange at the adjacent end-ofl the surrounding Grens-T lee and e eintesnenedend. insulated. frein saidv flange,. said. plates` of saidbyfpasscondensers being "adapted to be.' connected' respevc'tively ...to the positive plate voltage sourcer and. tfof the neg'.- ati-Ve l gridy voltage.. source, and .interconnected tubes-snrmnniI-s the less-of, said crees-T, 'eX- c'cfpt' for `por'ti'ons'of' Qsi'ibs'tantial,V length. `adjacent seid"bypass.Cendensersf seidfnertiene bei-ng ef. sueh lfengthfthatf. the.. c iective lengthA of. each of sai'dconductor's Will be substantially.one-:quarter Wave. length! atA the mid-bend frequency, whereby Seidfnelttiene Wi11=f0r1n .bien #nnnefnnee' Chnes at`.the.mid'.bandfrequency;' 1

5.` An"interstage coupling, for. arl-ulllhigh radio.. frequency lamplifierlcoifnprising, ,a branched tubular member, a, pair..ofconductorsrespectiyely extending 'coaxial-ly 'thron'gh.adj'acentnleg-'sofA said member,Y connectionsbetween each endfot ...ch ofv` said conductors and its. 'allacentcendV portion of. said 'croissfv-QT.; adftubular plateand vlline elements completely surrounding two legs of said member and partially surrounding the intermediate legs thereof, said tubular plate and grid line elements being interconnected and connected to said intermediate legs of said member, the exposed portions of said intermediate legs forming high impedance radio frequency chokes, the effective lengths of said conductors being substantially of one-quarter wave length at the midband frequency to be amplified.

6. An ultra high frequency circuit structure comprising a multi-leg tubular member, a pair of conductors each extending through a pair of adjacent legs of said member, a condenser formed between each end of each of said conductors and the adjacent end portion of its surrounding leg, and coupling lines in the form of a tubular part surrounding two legs of said member and surrounding a portion only of an intermediate leg, whereby the portion of said intermediate leg which is not surrounded by said coupling lines forms a radio frequency choke extension.

7. A circuit structure for use in interstage coupling of an ultra high frequency amplifier comprising, a multi-leg tubular member, a pair of conductors each extending through a pair of adjacent legs of said member, a tubular grid line and a tubular plate line respectivelsr surrounding a pair of legs of said member, a coupling stub surrounding a portion of another leg of said member and connected to said tubular grid and plate lines, a blocking condenser formed by a cap surrounding and insulated from the end of one of said pair of legs of said member, a similar blocking condenser at the outer end of the other of said pair of legs of said member, and a by-pass condenser formed at the end of another leg of said member, said by-pass condenser having one plate thereof formed by a portion of the leg.

GROTE REBER. 

